What you're looking for is BILATERAL SYMMETRY, meaning if the organism were cut in half down the middle, there would be two perfect sides. BI = 2, LATERAL = sides SYMMETRY. the other answer is wrong, the explanation is right but the term is wrong
One of the most prominent features of echinoderms is their radial symmetry. This means that if we divide the organism around any main axis it should be divided in two exactly similar halves across any plane passing through the body. This is because the mouth is surrounded by a central disk that contain specific structures called podia that radiate outwards and gives the radial symmetry to organism.
For example: The body of ctenophores, echinoderm, sea-anemone and many sponges have radial symmetry. Some echinoderms that have radial symmetry include sea urchin, Sea cucumber, bitter star etc.
